River Shannon
The River Shannon is the major river on the island of Ireland, and at in length, is the longest river in the British Isles. It drains the Shannon River Basin, which has an area of, – approximately one fifth of the area of Ireland.
Known as an important waterway since antiquity, the Shannon first appeared in maps by the Graeco-Egyptian geographer Ptolemy. The river flows generally southwards from the Shannon Pot in County Cavan before turning west and emptying into the Atlantic Ocean through the long Shannon Estuary. Limerick city stands at the point where the river water meets the sea water of the estuary. The Shannon is tidal east of Limerick as far as the base of the Ardnacrusha dam. The Shannon divides the west of Ireland from the east and south The river represents a major physical barrier between east and west, with fewer than thirty-five crossing points between the village of Dowra in the north and Limerick city in the south.
Course
By tradition the Shannon is said to rise in the Shannon Pot, a small pool in the townland of Derrylahan on the slopes of Cuilcagh Mountain in County Cavan, Republic of Ireland, from where the young river appears as a small trout stream. Surveys have defined a immediate pot catchment area covering the slopes of Cuilcagh. This area includes Garvah Lough, Cavan, to the northeast, drained by Pollnaowen. Further sinks that source the pot include Pollboy and, through Shannon Cave, Pollahune in Cavan and Polltullyard and Tullynakeeragh in County Fermanagh, Northern Ireland. The highest point in the catchment is a spring at Tiltinbane on the western end of the Cuilcagh mountain ridge.From the Shannon Pot, the river subsumes a number of tributaries before replenishing Lough Allen at its head. The river runs through or between 11 of Ireland's counties, subsuming the tributary rivers Boyle, Inny, Suck, Mulkear and Brosna, among others, before reaching the Shannon Estuary at Limerick.
Many different values have been given for the length of the Shannon. A traditional value is. An official Irish source gives a total length of . Some Irish guides now give. Some academic sources give, although most will refuse to give a number. The reason is that there is no particular end to a river that empties into an estuary. The 344 km length relates to the distance between Shannon Pot and a line between Kerry Head and Loop Head, the furthest reaches of the land. The 280 km distance finishes where the Shannon estuary joins the estuary of the River Fergus, close to Shannon Airport. Longer claimed lengths emerged before the use of modern surveying instruments.
At a total length of, it is the longest river in Ireland. That the Shannon is the longest river in the British Isles was evidently known in the 12th century, although a map of the time showed this river as flowing out of the south of Ireland.
There are some tributaries within the Shannon River Basin which have headwaters that are further in length than the Shannon Pot source's length of, such as the Owenmore River, total length in County Cavan and the Boyle River, total length with its source in County Mayo.
The River Shannon is a traditional freshwater river for about 45% of its total length. Excluding the tidal estuary from its total length of, if one also excludes the lakes from the Shannon's freshwater flow of, the Shannon, as a freshwater river, is only about long.
Apart from being Ireland's longest river, the Shannon is also, by far, Ireland's largest river by flow. It has a long-term average flow rate of . This is double the flow rate of Ireland's second highest-volume river, the short River Corrib are added to the discharge at Limerick, the total discharge of the River Shannon at its mouth at Loop Head reaches. Indeed, the Shannon is a major river by the time it leaves Lough Ree with an average flow rate of, larger than any of the other Irish rivers' total flow.
Distributaries
The main flow of the river is affected by some distributaries along its course, many of which rejoin it downstream. The Abbey River flows around the northeastern, eastern, and southern shores of King's Island, Limerick before rejoining the Shannon at Hellsgate Island.Protected areas
The Shannon Callows, areas of lowland along the river, are classified as a Special Area of Conservation.Settlements
Settlements along the river include Kilrush, Tarbert, Glin, Foynes, Askeaton, Shannon Town, Limerick, Castletroy, Castleconnell, O'Briensbridge, Montpelier, Killaloe, Ballina, Portumna, Banagher, Athlone, Lanesborough, Carrick-on-Shannon, Leitrim village and Dowra.Historical aspects
The river began flowing along its present course after the end of the last glacial period.Ptolemy's Geography described a river called Σηνος from PIE *sai-/sei- 'to bind', the root of English sinew and Irish sin ‘collar’, referring to the long and sinuous estuary leading up to Limerick.
Vikings settled in the region in the 10th century and used the river to raid the rich monasteries deep inland. In 937 the Limerick Vikings clashed with those of Dublin on Lough Ree and were defeated.
In the 17th century, the Shannon was of major strategic importance in military campaigns in Ireland, as it formed a physical boundary between the east and west of the country. In the Irish Confederate Wars of 1641–53, the Irish retreated behind the Shannon in 1650 and held out for two further years against English Parliamentarian forces. In preparing a land settlement, or plantation after his conquest of Ireland Oliver Cromwell reputedly said the remaining Irish landowners would go to "Hell or Connacht", referring to their choice of forced migration west across the river Shannon, or death, thus freeing up the eastern landholdings for the incoming English settlers.
In the Williamite War in Ireland, the Jacobites also retreated behind the Shannon after their defeat at the Battle of the Boyne in 1690. Athlone and Limerick, cities commanding bridges over the river, saw bloody sieges.
As late as 1916, the leaders of the Easter Rising planned to have their forces in the west "hold the line of the Shannon". However, in the event, the rebels were neither well enough armed nor equipped to attempt such an ambitious policy.
Navigation
1755 to 1820
Though the Shannon has always been important for navigation in Ireland, there is a fall of only in its first. Consequently, it has always been shallow, with depths in various places. The first serious attempt to improve navigability came in 1755 when the Commissioners of Inland Navigation ordered Thomas Omer, a new immigrant from England, possibly of Dutch origin, to commence work. He worked at four places between Lough Derg and Lough Ree where natural navigation was obstructed, by installing lateral canals and either pound locks or flash locks. He then continued north of Lough Ree and made several similar improvements, most notably by creating the first Jamestown Canal which cut out a loop of the river between Jamestown and Drumsna, as well as lateral canals at Roosky and Lanesborough.The lower Shannon between Killaloe and Limerick had a topography quite different from the long upper reaches. Here the river falls by in only. William Ockenden, also from England, was placed in charge of works on this stretch in 1757 and spent £12,000 over the next four years, without fully completing the task. In 1771 parliament handed over responsibility to the Limerick Navigation Company, with a grant of £6,000 to add to their subscriptions of £10,000. A lateral canal, long with six locks, was started but the company needed more funds to complete it. In 1791, William Chapman was brought in to advise and discovered a sorry state of affairs – all the locks had been built to different dimensions and he spent the next three years supervising the rebuilding of most of them. The navigation was finally opened in 1799, when over of corn came down to Limerick, as well as slates and turf. But even then, there were no tow paths in the river sections and there were still shoals in the summer months, as well as a lack of harbour facilities at Limerick, and boats were limited to load, often less.
With the approaching opening of the Grand Canal, the Grand Canal Company obtained permission from the Directors General of Inland Navigation, and asked John Brownrigg to do a survey which found that much of Omer's work had deteriorated badly, so they started repairs. After protracted negotiations on costs and conditions, the work was completed by 1810, so that boats drawing could pass from Athlone to Killaloe. Improvements on the lower levels were also undertaken, being completed by 1814.
When the Royal Canal was completed in 1817 there was pressure to improve the navigation above Lough Ree. The Jamestown Canal was repaired, harbours built and John Killaly designed a canal alongside the river from Battlebridge to Lough Allen, which was opened in 1820.
1820s to Independence
In the latter part of the 1820s, trade increased dramatically with the arrival of paddle-wheeled steamers on the river which carried passengers and goods. By 1831 14,600 passengers and of freight were being carried. This put new pressure on the navigation and a commission was set up resulting in the Shannon Navigation Improvement Act 1835 appointing five commissioners for the improvement of navigation and drainage who took possession of the whole navigation. Over the next 15 years, many improvements were made but in 1849 a railway was opened from Dublin to Limerick and the number of passengers fell dramatically. Freight, which had risen to over per year, was also halved.But the work the commissioners carried out failed to solve the problems of flooding and there were disastrous floods in the early 1860s. Given the flat nature of most of the riverbank, this was not easily addressed and nothing much was done until the 20th century.